• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

EL84 Amp - Baby Huey

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B

booth

Member
Joined 2010
Hi I am also a newbie and have been reading this thread for sometime. I began my build of the original version of the baby huey about a month ago and am very keen to see how good it sounds.

My question is about the Bias for the EL84 tubes. As it is unclear to me from the schematic which way round the Bias is connected. I've been doing a bit of reading to see if I can work it out.

From what I can gather the Cathode usually has a negative Bias but the grid should be negative with respect to the cathode. Otherwise there will be grid current. However, if grid is too negative wrt cathode (several volts) you come to the situation called cut-off where no current flows to plate or screen grid. In this circuit the grid is at 0 volts if no grid current is flowing. So does this mean I want the cathode to be positive? To have the Bias connected with the positive side to the Tubes?
 
Brouilly

Brouilly

Member
Joined 2009
I am currently mid Baby Huey build and am searching this vast thread for any posts of speaker choice. It seems that some are using the uFonkens....

What are people using for their Baby Hueys?

Being a novice DIYer im looking for plans for something to compliment my Baby Huey when it is finished.

Charlie
 
Soonerorlater

Soonerorlater

Member
Joined 2008
Booth,

That's a well thought out build, lots of useful photos for other builders - congrats.....:cool:

Charlie,

I'm using Monitor audio bronze, and sometimes some old Kef Coda 2's but would like to upgrade.

I was thinking of starting a separate thread to find out what speakers are attached to other peoples Baby Hueys, or indeed any pp EL84 amp, will wait and see the response here .::rolleyes:



Ps Wouldn't mind what Gingertubes got

:D
 
Brouilly

Brouilly

Member
Joined 2009
In the first time baby huey thread, gingertube says connect a 10ohm resistor from a 12v supply to the positive bias side, to check the circuit. You should read 0.4v across the resistor for 40mA current.

I am testing my circuit using the CCS winding (5v 3A) and a 470ohm resistor.

I read 5.28v across the resistor, ohms law tells me that's about 11mA current.

All 4 of my bias circuits read the same, so unless ive built all 4 wrong... I must be doing something else wrong...?

Can anyone help?

Thanks

Charlie

Still learning
 
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